High brightness mid-IR light sources have many applications in medicine, spectroscopy, ranging, sensing and metrology. Such sources need to be highly robust, have long term stability, and also comprise a minimal component count with a high degree of optical integration for mass market applications. Semiconductor laser based mid IR light sources are very popular. More specifically, quantum cascade lasers have become available that allow a high degree of integration. However, the requirement for cryogenic cooling is generally an obstacle and is not permissible for many applications.
High degrees of spectral coherence are also particularly important in the construction of frequency combs. Whereas laser sources operating in the near and mid infrared spectral region are readily available, very little work has been done on such frequency comb sources operating in the mid IR wavelength region.
Indeed, mass producible coherent fiber based mid-IR sources or mid-IR comb sources with a high spectral density and operating with a high degree of spectral coherence have not been produced to date.